1. Field of the Invention
The present invention concerns an environmental detection system particularly useful for fire detection and suppression which ensures high reliability in operation and high reliability in preventing false operation. More particularly, this invention is concerned with a microprocessor-based, software-driven control panel connected to one or more detector loops each of which includes a plurality of addressable detectors which send analog signals to the control panel representative of an environmental parameter such as smoke obscuration along with reference and identification signals. The control panel processes information received from the detectors to determine whether an alarm condition exists as defined by the system configuration defined in memory. The system provides automatic calibration and testing of the detectors, automatic testing under load of the backup batteries, flexibility in defining the protection scheme, and storage of history information concerning the system alarms and troubles. The preferred system also verifies alarm conditions before actuating an alarm or discharging a fire suppressant.
2. Background of the Prior Art
Typical prior art fire protection systems use fire detectors configured in a so-called detector loop which is coupled to a control panel. The detector loop comprises a pair of wires to which the detectors are electrically coupled in parallel. The wires are connected to the control panel which supplies operating power to the detector loop.
Fire detectors may be designed to sense smoke obscuration, ionization, temperature, or the like, all of which may be indicative of a fire. A typical detector is designed to operate in an on/off mode by changing from an inactive state to an active state whenever the environmental condition which the detector is designed to monitor exceeds a predetermined threshold. In the active state, the internal resistance of the detector is lowered thereby increasing the current flow therethrough and thereby increasing the current flow through the detector loop. When the current flow level in the detector loop exceeds a predetermined threshold, the control panel activates an alarm or discharges a fire suppressant such as water or halon, a fire suppressant gas.
This type of fire protection system presents a number of problems. For example, the sensitivity of each detector, that is, the threshold level which the detector changes from its inactive state to its active state, must be manually set by adjusting each individual detector. This task can become unwieldy and labor intensive in the typical system using hundreds of detectors. Additionally, the requirement to manually adjust the sensivity of each detector effectively prevents sensivity adjustment as a function of the time of day. For example, it may be desirable to have a low sensitivity in a kitchen area during the day when the kitchen is in use and producing some smoke and heat, and a high sensitivity, that is a low threshold level, at night when the kitchen is not in use.
Typical prior art systems also can be expensive to install if a so-called cross-zone protection scheme is to be used, for example. In the cross-zone scheme, a given area, such as a room, is defined as having two zones, each zone with its own detectors. The cross-zone scheme improves the reliability of the system by requiring that a detector from each zone be active in order to actuate the system which avoids a false alarm if a single detector becomes defective and thereby erroneously indicates an alarm condition. The cross-zone scheme also prevents a false alarm in the event of a short circuit in the wires of a single detector loop.
The cross-zone scheme, while improving the reliability of the system, is also expensive to install in that separate wires must be run for each detector loop. This can be particularly expensive if the area to be protected under the cross-zone scheme is a significant distance away from the control panel.
More recent prior art protection systems overcome some of the disadvantages of the older systems by providing a microprocessor-based control panel and so-called "smart" detectors. These detectors produce signals representative of the magnitude of the parameter being sensed, such as smoke obscuration, rather than just active-inactive signals. The control panel, typically under software control, analyzes the information sent from the detectors to determine whether an alarm condition exists. Additionally, the fire protection scheme can be defined in software which eliminates the need for separate detector loops and separate wiring for the various zones. That is to say, all of the detectors in a particular area can be part of a single detector loop with the zones defined in software for the cross-zone scheme, for example.
Even the more advanced prior art fire protection systems, however, present certain problems and disadvantages. For example, a typical detector experiences signal drift over time which may be due to dust accumulation on the components of the detector, the age of the components, and the ambient temperature surrounding the detector. Because of the signal drift, the detector can send incorrect information as to the magnitude of the parameter which the detector is sensing. In such circumstances, separate detectors exposed to the same environmental condition parameter may indicate different magnitudes. This in turn may cause a false alarm or even worse, fail to actuate an alarm when an alarm condition exists. To overcome this problem, manual calibration and testing of the detectors from time to time are required to maintain the reliability of the system. Accordingly, the prior art points out the need for a system which automatically calibrates and tests the detectors from time to time.
Typical prior art fire protection systems use conventionally available A.C. power to operate the system and include backup batteries to maintain the system in operation in the event of power failure. The capacity of the batteries decreases with age, however, which requires replacement on a timely basis. Determination of battery capacity requires manual testing by removing the batteries and placing them under load. This requires a conscientious and well developed maintenance program to ensure that these tests are periodically conducted. Accordingly, the prior art points out the need for a system which automatically and periodically tests the backup batteries under load to determine whether their capacity is sufficient to ensure reliable operation of the system in the event of power failure.
Finally, even the more advanced fire protection systems using microprocessors are subject to false alarms in the event the microprocessor fails to properly execute its operating program. That is to say, a voltage spike, induced currents caused by lightning, and so forth may cause improper execution of the operating program which may produce false actuation of a fire suppressant or alarm. Accordingly, the prior art points out the need for a system which verifies proper operation of a micro-processor-based control panel before an alarm output is produced.